I bought an '08 Legacy at an auction with a broken screen for the navigation. I'm looking to replace it. Some people have told me that I need to get the entire unit back and others that I only need to get the screen.

Do I need to get the entire unit or just the screen? Is there a way to check whether the GPS unit is still functioning?

Your screen can be exchanged for a working one through Kenwood. I don't know if you can work with them directly or if you have to go through a Subaru dealer. Expect to pay between $200-$300 for the exchange unit.